In recent years, market demand for energy saving and increases in speed has increased for image forming apparatuses such as printers, copiers, and facsimiles. With the increase of the market demand, also in the field of electrophotographic toner (hereinafter, may be simply referred to as “toner”), demand for a toner having excellent low-temperature fixing property increases, and at the same time, there is increased needs for a toner having property opposing to low-temperature fixing property, such as anti-offset property and heat resistance-storage stability (blocking resistance), increase.
In order to meet these demand and needs, a variety of toners using aromatic polyester resins are proposed, but they have a disadvantage in that they are poor in pulverizability in their production process. Then, to address the problem, a method is proposed in which a low-molecular weight polyester prepared using an aliphatic alcohol that is excellent in pulverizability as a monomer is blended with a highly polymeric polyester (see PTL1). However, when the low-molecular weight polyester prepared using an aliphatic alcohol is used, the heat resistance-storage stability of the toner is degraded because the polyester resin has a low glass transition temperature due to its structure and it is difficult to satisfy, at a high level, both low-temperature fixing property, anti-offset property and heat resistance-storage stability.
In contrast to this, a toner is proposed wherein as a binder resin a polyester resin is used which is composed of (i) an alcohol component composed of a branched-chain aliphatic alcohol, such as 1,2-propanediol and (ii) a carboxylic acid component (see PTL2 and PTL3). The toner exhibits excellent low-temperature fixing property when used in a wide variety of image forming apparatuses from conventional low-speed machines to high-speed machines, and the toner is excellent in that it can achieve, at a high level, both low-temperature fixing property, anti-offset property and heat-resistance storage stability. Since the toner is also excellent in pulverizability, it can advantageously achieve high productivity of a toner produced by pulverization.
Meanwhile, in recent years in the print industry, print on demand (POD) technology which does not require a step of plate making has been developed. It is anticipated that the POD technology using an electrophotographic printing method can be used as an alternative to simple printing technology (“keiinsatu”), because the POD technology is well suited for printing of a small number of copies and for variable printing. However, the printing market of the print industry requests a higher level of print quality than the conventional market requests for prints produced by conventional copiers, etc. The image forming apparatuses using the electrophotgraphic printing method have some points to be addressed in view of this fact. One of them is to meet demand for developing, for image forming apparatuses used in the POD technology, an ultra high-speed printing system that operates at a significantly faster printing speed than the conventional high-speed copiers. The other is to meet demand for developing a continuous form paper output system with which nonlimiting, a wide variety of recording media, including crimp postcards, pre-printed forms, and address labels for direct mails can be processed. Thus, it further becomes necessary to meet demand for a toner which has excellent fixing property even with smaller heat input than the heat input which has been provided for a low-temperature fixing toner such as used in conventional copiers. Particularly when pages of printed forms or bound printed matter are flipped over and the printed images thereon are strongly rubbed by the user's hand, the user's hand or the printed images on the pages is easily smeared with the toner, which requires the printed images on the printed forms or bound printed matter to have more excellent smear resistance than the images printed by means of conventional copiers. In other words, it further requests the fixed images to have a low friction coefficient (reduction in μ of the fixed images).
In contrast to this, a toner is proposed wherein the fixing property of the toner and the smear resistance of the fixed images are increased by incorporating an alkylene oxide compound having a particular structure into the toner (see PTL4 and PTL5). However, the alkylene oxide compound is used as a surfactant in these proposed toners, and this process is only applicable in practice to a method in which a toner is polymerized and is ineffective for a method in which a toner is kneaded and pulverized.
Furthermore, a toner is proposed wherein a crystalline polyester resin and as an external additive a fine fluorine resin powder are used (see PTL6). However, in the proposed toner the fine fluorine resin powder decreases low-temperature fixing property, as well as, in the production process of the proposed toner, the proposed toner using the crystalline polyester resin exhibits poorer pulverizability than the toner using a polyester resin containing an aliphatic alcohol and an additional step of controlling the degree of crystallization is required.
Therefore at present it is desired that a toner is provided which may achieve both low-temperature fixing property, anti-offset property, and heat-resistance storage stability at such a level that the toner can be used in an ultra high-speed fixing system, can achieve particularly a low friction coefficient in fixed images (reduction in μ of the fixed images), and has excellent productivity.